The best books about jiu jitsu are 1. Jiu-Jitsu University by Saulo Ribeiro; 2. Breathe: A Life in Flow by Rickson Gracie; 3. 5 Rules for White Belts by Chris Matakas; 4.The Black Belt Blueprint: An Intelligent Approach to Brazilian Jiu Jitsu; 5. Mastering the 21 Immutable Principles of Brazilian Jiu-Jitsu by Paulo Guillobel
1. Using Egg whites
2. Greek Yogurt with Mio/Stevia or another low calorie sweetener
3. Lean Ground Turkey with Pasta and Pasta Sauce
Yes, it is strongly recommended to train both bjj and muay thai at the same time. Especially, if you are looking to become a well rounded martial artist but as always you should make recovery a priority.
The best martial arts for self-defense is a combination of Brazilian Jiu jitsu, Muay Thai, and wrestling. An effective martial art should include live sparring and high level competition.